(1) Field of the Invention
The present invention relates to a method and system for coating internal passages within a turbine engine component.
(2) Prior Art
High pressure turbine blades, vanes, and seals operating in today's gas turbine engines are life limited by both thermal fatigue cracking on the airfoil and coating defeat due to oxidation from high operating temperatures. The need for good oxidation resistance on the airfoil necessitates the application of a suitable oxidation resistance coating such as a MCrAlY metallic overlay coating with increased oxidation resistance and/or a thermal barrier coating system for temperature reduction. Internal oxidation and corrosion have been experienced in turbine engine components such as high pressure turbine blades or vanes. Thus, there is a need to coat the internal surfaces of these turbine engine components for protection from the operating environment. Vapor phase aluminizing processes in use today do not allow the coating of internal surfaces without applying a standard thickness coating on the external surface of the turbine engine component at the same time. The presence of an external aluminide with either a MCrAlY overlay or a thermal barrier coating on top is not desirable and may reduce the thermal fatigue resistance of the turbine engine component.
Current coating processes for applying a vapor aluminide coating to the internal surfaces of the turbine engine component requires a flow of an aluminum halide gas directed through the internal passages of a hollow airfoil. Complete coating coverage of all internal surfaces is a function of how well the gas flows through and contacts all surfaces on the interior of the turbine engine component. Complete internal coverage often requires all openings to the exterior of the turbine engine component, i.e. trailing edge slots, casting chaplet holes, airfoil cooling holes, tip cooling holes, etc., to remain open during the coating process. Most internally coated turbine engine components require coating coverage in these cooling features as well. Currently, there is no effective way to mask the external surfaces of a blade to prevent aluminide deposition on the external surfaces while insuring full coating coverage on all internal surfaces because of the necessity to have the openings in the turbine engine component remain open for gas flow.